diff --git a/src/main/java/alfio/extension/ExtensionService.java b/src/main/java/alfio/extension/ExtensionService.java
index 2837438c55..71800ebacb 100644
--- a/src/main/java/alfio/extension/ExtensionService.java
+++ b/src/main/java/alfio/extension/ExtensionService.java
@@ -212,6 +212,7 @@ public <T> T executeScriptsForEvent(String event, String basePath, Map<String, O
         T res = null;
         Map<String, Object> input = new HashMap<>(payload);
         input.put("extensionEvent", event);
+        input.put("output", null);
         for (ScriptPathNameHash activePath : activePaths) {
             String path = activePath.getPath();
             String name = activePath.getName();